Ballpoint pens typically have hard tip balls mounted in nibs made of formable material. When mounting the hard balls in their seat in the nib of the ballpoint pen, the balls are first inserted into a generally cylindrical blind hole and then the edge of the nib that extends above the equator of the ball is flanged by plastic deformation so as to surround and to hold the ball in the zone “above” the equator.
The hole in which the ball sits has sockets or grooves in its inner end region to allow the writing fluid (hereinafter termed “ink” for simplicity) to be transported. Nor is the hole actually blind, because from its inner end region a bore whose diameter is less than that of the ball leads to the ink reservoir.
The flanging of the edge has been carried out for many years by, for example, the following method disclosed in U.S. Pat. No. 3,135,231. The flanging device, termed the rotating head, has two rods set parallel to and spaced part from each other and oriented in the vertical direction. At their lower ends, the rods support hard forming disks of circular shape which taper generally conically in a downward direction. The assembly formed by the rod and the forming disk is known as the rotating roll and is installed in such a way as to be able to pivot freely. The peripheries of the forming disks comprise a small interval in the form of a gap. In the center of this gap is a hard, thin tongue with a V-shaped end surface that can move axially against a spring. The rotating head can rotate about the axis of symmetry of the two shafts of the forming disks and is also rotated about this axis.
The method of operation is thus as follows. A nib with its ball is guided coaxially relative to the axis of rotation of the rotating head in the gap between the forming disks and the ball then firstly contacts the V-shaped front surface. The ball and the nib are thus positioned centrally and securely in the plane of the tongue. The tongue is then displaced against its spring and the nib arrives in contact with the forming disks installed in such a way as to be able to pivot freely. This results in centering in the plane normally with respect to the plane of the tongue. The axial compression of the nib and of the rotating head against each other takes place with a predefined force as a result of a predefined number of relative rotations. The relative movement between the nib and the rotating head produces an offset in terms of rotation of the forming disks. Thus, because of the compressive force and because of the series of rotations, the edges of the forming disks are compressed against the ball and the formable material of the edge is densified and drawn, which creates an approximately concentric gap around the ball in the area of the equator. The flanging operation is thereby completed.
This apparatus is tried and tested and more than half of all ballpoint pens made worldwide are made by this process and with such devices.
This device does however have a drawback which is due to the predefined geometrical ratios of size within narrow limits of the various components. Because there are two shafts oriented parallel to the forming disks, it is impossible, even with extreme miniaturization and using special flat-mounting bearings in the radial direction, to achieve a gap between the two axes of rotation that is less than about 10 mm. The diameters of the forming disks are thus also unavoidably fixed at approximately 10 mm each. The nib usually has a diameter of about 0.6 to 1.2 mm in the region of its edge and it is therefore sharply curved. The nib: forming-disk-curvature ratios thus range from about 1:16 to 1:8. These size ratios result in a relatively large contact area and thus a low Hertz surface pressure. With a higher Hertz surface pressure there is better “kneading” of the nib material. The most effective way to achieve this is to reduce the contact area, which can be done by increasing the ratio of curvature to 1:4 for example.
Another drawback of the already known device is that it is difficult to adjust the axial position of the two forming disks accurately.
U.S. Pat. No. 3,135,231 also discloses an embodiment in which the two rods of the forming disks are not arranged parallel to the axis of rotation of the rotating head, but obliquely to the latter, so that their axes intersect the axis of rotation. The reason for this arrangement is not indicated, nor is it used in practice probably because of the high cost of manufacture of non-parallel seats for the bearings of the rods.